This invention relates to camshafts having cams which can move angularly to a limited extent on the camshaft.
Limited angular motion of individual cams on a camshaft is important to provide, for example, variable valve lift curves for the intake valves of an internal combustion engines. German Patent No. 32 34 640 and German Offenlegungsschrift No. 41 00 087 disclose camshaft arrangements of this kind for intake valves of internal combustion engines in which the limited angular motion of the cams relative to the camshaft on which they are mounted permits a relatively broad valve lift curve to be produced at high engine speeds, but a narrow valve lift curve at low speeds. This is accomplished by displacement of the valve closing time, the ascending flank of the lift curve being independent of rotational speed. In principle, however, it is possible instead to design such a camshaft arrangement so that the ascending flank of the valve lift curve is variable.
The limited angular motion of the cam is permitted by providing an angular recess in the cam adjacent to the camshaft so that an element projecting from the shaft is angularly movable in the recess. To assure a continuous valve lift curve and to avoid any interruption of contact between the cam surface and the valve, it is important to provide a damping fluid in the angular recess accommodating the projecting element. This in turn requires a seal capable of retaining the damping fluid at every speed range of the camshaft, i.e., at all engine speeds.
Insofar as the above-mentioned prior art discloses any solution to this problem, for example, German Offenlegungsschrift No. 41 00 087, there are comparatively few designs for angularly movable cams.
Another problem to be considered is the prevention of excessive friction between the cam-driving element associated with the camshaft, which has a flat outer surface in the prior art arrangements, and the adjacent inner surface of the angular recess in the cam. This is especially important when the projecting element comprises an additional contoured part which is inserted in a camshaft groove extending parallel to the axis of the camshaft and is subject to centrifugal forces, as in the arrangement disclosed in German Patent No. 32 34 640. If the cam-driving element is integral with the camshaft or is a constituent part of the shaft, as in the arrangement described in German Offenlegungsschrift No. 41 00 087, extremely precise fabrication is required to avoid undesirable wear.